But Stross is definitely not translating Graeber into fiction -- in fact, he thinks his ending kind of sucks, because he couldn't figure out an ending which "repudiated the entire framework of inherited debt without simultaneously getting all preachy on a soapbox."
On the other hand, Neptune's Brood does contain the rudiments of a very interesting critique of the notion of liquidity. Liquidity is the ease with which something can be converted into purchasing power. Cash is generally accepted so it is highly liquid, buyers for treasury bonds are usually plentiful so treasury bonds are pretty damn liquid, a pile of gold in a geopolitically unstable jungle might be somewhat less liquid (compare Neal Stephenson's Cryptonomicon), a stolen artwork might be even less liquid, etc.
But really, the "ease" with which something can be converted into something else isn't just a function of what the thing is: it's a function of who owns it, and in what ways, and what they want to convert it into, and what they want to convert that into, and many other factors. The problem with the notion of liquidity is that it collapses all these innumerable factors into a single scale.
In Neptune's Brood there are three kinds of money: fast, medium, and slow. There is a sense in which fast money is highly liquid, medium money is somewhat liquid, and slow money is scarcely liquid at all. Slow, in fact, sort of means illiquid. But what is striking about thinking through these currencies is the qualitative shifts involved. Slow money is essentially implicated with a different kind of activity. An economic anthropologist might say that it constitutes its own sphere of exchange or its own transactional order. That is, slow money is "the currency of world-builders," used for financing star ships and colonies.
It takes power and expert labor to run an interstellar communications laser beacon – lots of both. Nobody will point a laser at a new colony and beam libraries of design templates and cohorts of expert soul dumps at them without an expectation of getting something in return. All colonies must of necessity go deep into debt in the decades after their foundation: It costs a lot of slow money to acquire the vital new technologies and skills it needs to plug unforeseen gaps. Only once its population has increased enough to support a local education, research, and development infrastructure – which can take centuries – can it aspire to a trade surplus.Stross plays on the relative causal isolation which exists on the vast interstellar scale to pose interesting questions about the nature and limits of liquidity. Is a currency zone encompassing worlds so far apart even an intelligible notion? Is slow money really money? Does it circulate? Does it have purchasing power? Is it really slow: that is, can its illiquidity really be meaningfully related to the system of light-speed-constrained, third-party-notarization banking which Stross imagines, which is what makes slow money transactions take so long? And does the "slowness" of slow money intuitively connote "stability" because we now strongly associate instability and speculation, including lightning fast automated High Frequency Trading? I suspect that, like many of science fiction's most useful extrapolative thought experiments, the value of Stross's model is in how interestingly it disintegrates when closely considered.
Here's a friendly critique of Neptune's Brood from Robin Hanson. I also grapple with slow money here and especially here. See also entry for David Graeber.